1. Field of the Invention
This invention relates to a composite head comprising a read head using magnetoresistive effect and an inductive recording head, more particularly to a magnetoresistive effect composite head (hereinafter referred to as "composite head") of high density having a track width of less than 2 .mu.m and a magnetic storage apparatus using the same.
2. Description of the Related Art
Recently, a magnetoresistive effect type head (hereinafter referred to as MR head) has been more and more demanded because a relative speed between a magnetic reading head and a magnetic recording medium has been decreased with accelerated reduction of size of the magnetic recording medium and increased capacity thereof. This MR head has been discussed under a title of "A Magnetoresistivity Readout Transducer" of "IEEE Trans. on Magn,. MAG7(1970) 150".
Further, a giant magnetoresistive effect (hereinafter referred to as GMR) type head using giant magnetoresistive effect capable of realizing a higher output than the aforementioned MR head has attracted much attention these days. In this GMR head, particularly magnetoresistive effect generally called spin valve effect, that a resistance change corresponds to cosine between magnetizing directions of two adjacent magnetic layers, causes a large change in resistance with a small operating magnetic field. Thus, this GMR is expected to be the next generation MR head. The MR head using this spin valve effect has been discussed under a title of "Design, Fabrication & Testing of Spin-Valve Read Heads for High Density Recording" in "IEEE Trans. on Magn,. Vol.30, No.6(1994)3801". As stated in this paper, one magnetic layer of the two magnetic layers generating spin valve effect acts as a magnetization fixing layer, in which magnetization is fixed to substantially agree with the direction of medium magnetic field entering a head sensitive portion by switched connection, which is caused by overlaying antiferromagnetic film on this magnetic layer. Then, another magnetic layer adjacent to the aforementioned one through this magnetization fixing layer and conductive layer such as Cu is a magnetization free layer, in which magnetization direction can be changed freely relative to medium magnetic field.
Actually, a laminated structure for generating this spin valve effect is used as the composite head shown in FIG. 42. FIG. 42 is a schematic view of the structure of the composite head taken from air bearing surface (ABS) which is a face opposing a medium. That is, a laminated structure for generating spin valve effect is formed by disposing a central region 16 through magnetic separating layers 13, 17 made of insulators between the lower shield 12 and upper shield 18, which are overlaid on a ceramic 11 which acts as a slider. On both sides of this central region 16 are formed end portion regions 14, 15 for supplying current and bias magnetic field to the central region 16. That aforementioned spin valve element executes reproduction. Further, the upper shield 18 serves as a first magnetic pole 18a and then a second magnetic pole 110 is overlaid on a surface opposite to the spin valve element, of this magnetic pole 18a through a magnetic gap 19 such that the second magnetic pole 110 is in parallel to the magnetic pole 18a. A coil (not shown) surrounded by insulator is disposed deeper than the magnetic poles 18a, 110, so that recording is carried out by magnetic flux leaking from the magnetic gap 19 between the magnetic poles 18a and 110 magnetized by a magnetic field generated by this coil. Such a structure in which the read MR head and recording inductive (hereinafter referred to as ID) head are overlaid is a composite head using practical spin effect.
Meanwhile, the recording density under which the composite head using the spin valve effect is actually used is considered to be high density recording region of more than 3 GB per 1 square inch. In recording density lower than this, a composite head employing the MR head using magnetic anisotropy has been used since before. Namely, a spin valve head meaningful in practical field is limited to one achieving high density recording/reproduction of more than 3 GB per 1 square inch. A magnetic recording apparatus build using the spin valve head is a high density recording/reading apparatus of more than 3 GB per 1 square inch.
Basically patterning technology for determining the central region 16 which serves as a reproducing track width of the spin valve head can utilize semiconductor technology because this technology must only correspond to thin spin valve film or the like. By using i-line stepper, sub-micron level patterning can be achieved. On the other hand, the width of a front end portion of the magnetic pole 110 for determining the recording track width on the ABS is required to be narrow.
However, in a conventional ID head process, namely, in such a process in which the magnetic pole 18a is formed, then a coil covered with insulator layer is formed and the magnetic pole 110 is formed, frame resist for determining an external shape of the magnetic pole 110 must be formed in a condition that it rides over the coil covered with the insulator layer having a large step difference. Further, narrowing of the end portion of the magnetic pole 110 for determining the recording track width is difficult because it is located very near the end portion of the insulator layer, so that its limit is about 2 .mu.m. To achieve a high density recording of more than 3 GB per 1 square inch, a recording track width of less than 2 .mu.m, actually less than 1.5 .mu.m is needed. Therefore, in the conventional ID head process, it is difficult to produce a composite head meaningful in practical field using the spin valve effect.
As a method for surpassing the limit of the front end width of the second magnetic pole of this ID head, Japanese Patent Application Laid-Open No. 7-225917 has disclosed a method in which only the front end portion of the second magnetic pole for determining the track width is formed before formation of the coil covered with the insulator layer and then the coil and remaining second magnetic pole entirely are formed. It is generally said that, according to this method for forming the front end portion of the second magnetic pole first, a second magnetic pole having a narrow end width of about 1 .mu.m can be produced. FIGS. 43, 44 are sectional views of the ID head stated by the aforementioned patent publication. Referring to FIG. 43, the second magnetic pole comprises a main body portion 24 and a front end portion 23, the front end portion 23 being produced first. In FIG. 44, the second magnetic pole comprises a main body portion 34 and a front end portion 33. The front end portion 33 is properly positioned on a front end portion 31b of the first magnetic pole through a magnetic gap 32 in the width direction thereof. In FIGS. 43, 44, the front end portions 23, 31b, 33 for determining the recording width are patterned by ion beam etching before insulator layers 25, 35 are formed. That is, according to this method, the zero height position is determined by patterning when the front end portions 23, 33 of the second magnetic pole are formed.
However, if the ID head is produced actually in this method, following two fatal faults occur although they are not estimated in the aforementioned patent publication.
One of them is that, as for the front end portion of the second magnetic pole (hereinafter referred to as magnetic pole front end portion) produced first, if considering in viewpoints of cost, patterning by frame plating method is much more advantageous than patterning by ion beam etching. However, because if the magnetic pole front end portion is formed by this frame plating method, the magnetic pole front end portion is determined at throat height (length from an end of the insulator layer covering the coil up to ABS) zero, the resist shape for forming a frame is enclosed in the U-shape. Therefore, if a magnetic pole of NiFe is formed by ordinary paddle plating, plating solution cannot flow sufficiently into this enclosed portion. As a result, the composition of the formed plating film changes so that the magnetic characteristic of the magnetic pole front end portion requiring the best magnetic characteristic is deteriorated or deviated. Consequently, abnormal phenomenon occurs in generation of magnetic flux at the magnetic pole front end portion, so that the recording characteristic is deteriorated or deviated thereby leading to a large reduction of yield rate.
Another point is that in the second magnetic pole, deviation of the throat height becomes very large. The throat height length must be strictly controlled because it affects largely the recording characteristic such as overwrite characteristic of the ID head. However, in this head, the resist shape for forming the frame is enclosed in the U shape and further the gap of this enclosed portion is as small as less than 2 .mu.m. As a result, the inside angle of this enclosed portion and resist width deflect, so that substantial control of the throat height length is impossible. Thus, yield rate is largely reduced. In conclusion, as described above, a method for producing first the magnetic pole front end portion which determines the recording track width as a process considering production cost has not been yet established.